1. Field of the Invention
The present invention relates generally to the art of window coverings, and more particularly to the types of window coverings which include a head rail, a bottom rail and lift cords, such as horizontal blinds, pleated shades, cellular window coverings, Roman shade products, light control window coverings and the like. In its most preferred form, the present invention relates to a system for adjusting the length of the lift cords using a mechanism located within the bottom rail, so that in a fully lowered position, the bottom rail will hang at a desired distance from the head rail and will be level.
2. Description of the Prior Art
A wide variety of different types of window coverings are known which include lift cords. Familiar examples include horizontal venetian-type blinds, sometimes referred to as mini-blinds, pleated shade window coverings, cellular window coverings, various light control products and certain Roman shade products. Typically, such window coverings include a head rail mounted at the top of a window, window covering material coupled to or suspended from the head rail and a bottom rail coupled to the lower end of the window covering material or supports therefor. With venetian-type blinds, a ladder system is employed to suspend a plurality of slats in a horizontal orientation between the head rail and bottom rail, and two or more lift cords are passed through each slat from the bottom rail to the top rail. Typically the lift cord passes through holes in each slat, although other systems are known in the art. Most frequently, the lift cords are directed by pulleys or other mechanisms in the head rail to one end of the head rail, at which point they descend along one side edge of the window covering so that they can be manipulated by the user. By pulling on the lift cords, the bottom rail is moved toward the top rail, with corresponding accumulation of slats on the bottom rail as upward movement continues.
Similar lift cord systems are used in a variety of the "soft" window products which are currently popular, including window coverings which have pleated fabric between the head rail and the bottom rail, window coverings which have cellular fabric material between the head rail and the bottom rail, light control products which include cells having opaque portions arranged between the bottom rail and the head rail for light control and the like.
Systems are also known wherein the lift cords may accumulate on spring motor reels within the head rail so that they do not exit the head rail at all. Such a system is shown in U.S. Pat. No. 5,482,100 issued Jan. 9, 1996 to Kuhar entitled "Cordless, Balanced Venetian Blind Or Shade With Consistent Variable Force Spring Motor". This system uses spring motors to balance the weight of the bottom rail and the accumulating window covering material as the window covering is raised or lowered by simply grasping the bottom rail and urging it upwardly or downwardly.
One problem common to such window coverings is the adjustment of the lift cords so that the window coverings may be deployed a predetermined amount. For example, with most window coverings, it is desired that in the fully lowered position, the bottom rail will extend across the window sill and be spaced a small distance above it. Because it is practically impossible to manufacture window coverings in all possible lengths, fabricators or installers typically adjust the lift cord length in accordance with specific instructions, thereby adding to the ultimate cost to the consumer. A variety of techniques are well-known in the art for adjusting the length of the lift cords, including various mechanisms within the bottom rail to which the lift cords are attached and to which the lift cords can be adjustably secured for the proper length. Many of such systems are complex, making it difficult to quickly and inexpensively achieve the desired adjustment. Some mechanisms adjust both lift cords, while other adjust one lift cord which, in turn, is coupled to the other lift cord thereby providing equal adjustment.
While known systems do provide length adjustment, they suffer from one or more drawbacks with regard to installation and/or use. For example, it may be necessary, if a window covering is to be used at a new location, to re-adjust the length of the lift cords for that particular window to achieve the desired aesthetic result. An untrained user may not be able to provide such adjustment in an accurate manner.
A system for adjusting the length of lift cords in window coverings which would be easily understood and used by consumers would represent a significant advance in this art.